Fuel cells are a safe, environmentally friendly source of electric energy for portable devices, vehicles (including hybrid vehicles), generators, and aerospace and military applications. The current technology of fuel cells, however, has not made a significant impact on the mainstream market due to cost, size, and the lack of an immediate need to replace current power sources, such as batteries and gasoline- or diesel-powered internal combustion engines. The long-term need to find alternative power sources has become increasingly evident, however. For example, the byproducts of gasoline- and diesel-powered internal combustion engines are environmentally harmful. In contrast, the byproducts of fuel cells are clean, and in some cases, comprise only water.
Further, with portable electronic devices, such as cell phones, laptops, and handheld personal organizers becoming smaller, the need for smaller power sources, such as micro fuel cells, becomes evident. Present fuel cell technology, however, typically requires large fuel cell stacks comprising high-cost flat proton exchange membranes (PEMs).
Additionally, consumer products require power sources that operate for an extended period of time without the need for recharging. Micro fuel cells typically provide a longer lasting energy output with one cartridge of fuel. For example, the chemical fuels used in micro fuel cells promise to power devices up to ten times as long as batteries on a single charge. Further, once the energy source becomes low, the energy level can be restored by merely replacing the fuel cartridge.
Most fuel cells employ a copolymer of tetrafluoroethylene (TFE) and a perfluorinated monomer comprising sulfonic acid groups, such as perfluorosulfonyl fluoride ethoxy propyl vinyl ether (PSEPVE). One such copolymer is available as NAFION® (E. I. duPont de Nemours and Co., Wilmington, Del., United States of America), or a similar commercially available material. These materials often are provided as a membrane in final form, e.g., a non-thermoplastic form having a flat rectangular or square geometry, for subsequent use. If the membrane is flat and smooth, i.e., non-patterned, the catalyst layer also must be flat. Further, such membranes typically must be of at least a certain minimum thickness to be handleable. Additionally, the power density or conductivity is usually directly proportional to the membrane thickness; that is, the thicker the membrane, the lower the power density.
Additionally, Lu et al., Electrochimica Acta, 49, 821-828 (2003) have described silicon-based materials for use in a micro direct methanol fuel cell. Silicon-based micro direct fuel cells are rigid, brittle devices that typically are expensive and time consuming to manufacture. Also, incorporating actuating valves in silicon-based materials is difficult or impossible due to the rigid nature of the material. Further, the silicon-based micro direct methanol fuel cell described by Lu et al. has a ratio of active area versus macroscopic area equal to about one.
Also, in currently available fuel cell technologies it is imperative to have good contact between the electrode, proton exchange membrane (PEM), and catalyst. High power densities rely on conformal contact between the electrode, the catalyst, and the PEM. Much research has been invested in developing new PEMs and new catalysts, but little has been investigated in terms of a new catalyst ink composition. Conventional catalyst inks or tie layers typically consist of a catalyst such as platinum, an electrode material such as carbon black, and a dispersion of NAFION®, water, and alcohol.
Further, PEMs currently available in the art consist of one equivalent weight (EW), which gives rise to a trade-off between power density and methanol permeability.
Thus, there is a need in the art for an improved electrochemical cell, in particular a micro fuel cell that is capable of providing power to small, portable electronic devices, as well as a need for improved electrochemical cell components.